Add note about event type feature flags backwards compatibility

Author: svix-lucho

docs/event-types.mdx

@@ -1176,10 +1176,16 @@ curl -X POST "https://api.us.svix.com/api/v1/event-type/user.signup/" \
 </CodeTabs>
 
 :::info[Important]
-Keep in mind that endpoints with no event type filtering will receive all messages regardless of feature flags. Also, users with knowledge of a feature flag-gated event type can subscribe to that event type regardless of feature flags.
+Keep in mind that endpoints with no event type filtering will receive all messages regardless of feature flags.
+
+Users with knowledge of a feature flag-gated event type can subscribe to that event type regardless of feature flags.
 Feature flags only impact event types' visibility in the catalog and the API, not their deliverability.
+
+For backwards compatibility, when adding a feature flag to an existing event type, users that are already filtering by that
+event type in one of their endpoints will still see it in the Event Catalog and the API.
 :::
 
+
 ## Appendix
 
 ### Generating an OpenAPI spec